The present invention relates to a projection type cathode ray tube device used for a projection type image display device such as a projection TV receiver and a video projector.
The projection type image display device incorporates three projection type cathode ray tube devices for producing red, green and blue images, respectively. The three images on the projection type cathode ray tube devices are enlarged by a projection lens and are combined on a screen.
Each of the projection type cathode ray tube devices incorporates a deflection yoke, a convergence yoke, and an alignment magnet arranged in the order from a phosphor screen toward an electron gun. An electron beam projected from the electron gun is deflected by a deflection magnetic field generated by the deflection magnetic field, and then reaches the phosphor screen.
Distortions of the rasters and size differences between the three color rasters (called color misregistration or misconvergence) projected on a viewing screen are corrected by magnetic fields generated by convergence yokes. In the projection type image display device, three images projected from the three projection type cathode ray tubes need to be made coincident on the viewing screen, and therefore a convergence yoke needs to be employed to obtain images free from color misregistration. Such a conventional technique is disclosed in Japanese Patent Application Laid-Open No. Hei 8-287845, for example.
Recently, projection type cathode ray tubes having a neck composed of different-diameter portions (hereinafter projection type CRTs of the different-diameter multiple neck type) have been developed which makes an outside diameter of a deflection-yoke-mounting portion smaller than that of a portion housing an electron gun, for the purpose of achieving the reduction of a deflection power consumption and the improvement of focusing characteristics at the same time.
In the projection type CRTs of the different-diameter multiple neck type, when a convergence yoke for correcting the above-mentioned color misregistration is mounted around the portion of the neck having the smaller outside diameter (the small-diameter neck portion), the sensitivity of correction of color misregistration on the viewing screen of the projection type image display device is improved because the inside diameter of the convergence yoke itself is reduced. In this case, however, since it is necessary to increase the axial length of the small-diameter neck portion for providing the space for mounting both the deflection yoke and the convergence yoke, a main lens of the electron gun housed within the portion of the neck having the larger outside diameter (the large-diameter neck portion) is moved farther from a phosphor screen, and therefore focus characteristics on the phosphor screen is degraded. Moreover, when the axial length of the small-diameter neck portion is increased, the overall length of the projection type cathode ray tube itself is increased, and it is not desirable for realizing a compact projection type image display device.
Under these circumstances, in the projection type CRTs of the different-diameter multiple neck type, it is inevitable to mount the convergence yoke around the large-diameter neck portion, and therefore it has been a problem of improving the sensitivity of correction of color misregistration.
A representative purpose of the present invention is to provide a projection type cathode ray tube device employing a projection type CRT of the different-diameter multiple neck type having improved focus characteristics of an image display and improved efficiency of correction of color misregistration.
A representative configuration of the present invention is such that, in the projection type CRTs of the different-diameter multiple neck type, a convergence yoke is disposed to extend from the large-diameter neck portion to the transition region between the large-diameter and small-diameter neck portions.
Since projection type cathode ray tubes employ a single-color phosphor screen and a single-beam electron gun, they have larger space between the electron beam and the inner wall of the neck of their vacuum envelope than color cathode ray tubes employing a three-color phosphor screen and a three-beam electron gun, and therefore, in the projection type cathode ray tubes, there is not much possibility that the electron beams strike the inner wall of the neck. In view of this, in the projection type CRTs of the different-diameter multiple neck type, a difference between the large-diameter and small-diameter neck portions are made as large as possible to realize reduction of deflection power consumption and improvement of focus characteristics effectively.
On the other hand, the diameter of the neck varies gradually along the axis of the neck in the neck junction region between the large-diameter and small-diameter portions, and therefore the axial length of the neck junction region is increased as the difference between the large-diameter and small-diameter neck portions is increased. Space around the neck junction region has not been used effectively. The above-mentioned representative configuration of the present invention uses the otherwise unused neck junction region as space for mounting the convergence yoke effectively, thereby increases the axial length of the convergence, and increases the efficiency of correction of color misregistration without mounting the convergence yoke around the small-diameter neck portion intentionally.
In accordance with an embodiment of the present invention, there is provided a projection type cathode ray tube device comprising: a glass envelope including a panel, a neck, a funnel connecting the panel to an end of the neck, and a stem closing another end of the neck; a phosphor screen formed on an inner surface of the panel; an electron gun housed in the neck for projecting an electron beam toward the phosphor screen; a deflection yoke for scanning the electron beam on the phosphor screen; and a convergence yoke for generating a beam-convergence magnetic field, wherein the neck comprises a small-diameter neck portion disposed on a side thereof facing toward the funnel, a large-diameter neck portion disposed on a side thereof facing toward the stem, and a neck junction region connecting the small-diameter neck portion and the large-diameter neck portion; the deflection yoke is disposed in a vicinity of a transition region between the funnel and the small-diameter neck portion, and the convergence yoke is disposed to extend from the large-diameter neck portion and surround at least a portion of the neck junction region.
In accordance with another embodiment of the present invention, there is provided a projection type cathode ray tube device comprising: a glass envelope including a panel, a neck, a funnel connecting the panel to an end of the neck, and a stem closing another end of the neck; a phosphor screen formed on an inner surface of the panel; an electron gun housed in the neck for projecting and focusing an electron beam onto the phosphor screen; a deflection yoke for scanning the electron beam on the phosphor screen two-dimensionally; and a convergence yoke for generating a beam-convergence magnetic field, wherein the neck comprises a small-diameter neck portion disposed on a side thereof facing toward the funnel, a large-diameter neck portion disposed on a side thereof facing toward the stem, and a neck junction region connecting the small-diameter neck portion and the large-diameter neck portion; the deflection yoke is disposed in a vicinity of a transition region between the funnel and the small-diameter neck portion, the convergence yoke is disposed around the neck junction region, and an inside diameter at a phosphor-screen-side end of the convergence yoke is smaller than an outside diameter of the large-diameter neck portion.
In accordance with another embodiment of the present invention, there is provided a projection type cathode ray tube device comprising: a glass envelope including a panel, a neck, a funnel connecting the panel to an end of the neck, and a stem closing another end of the neck; a phosphor screen formed on an inner surface of the panel; an electron gun housed in the neck for projecting an electron beam toward the phosphor screen; a deflection yoke for scanning the electron beam on the phosphor screen; and a convergence yoke for generating a beam-convergence magnetic field, wherein the neck comprises a small-diameter neck portion disposed on a side thereof facing toward the funnel, a large-diameter neck portion disposed on a side thereof facing toward the stem, and a neck junction region connecting the small-diameter neck portion and the large-diameter neck portion; the deflection yoke is disposed in a vicinity of a transition region between the funnel and the small-diameter neck portion, and the convergence yoke is disposed around the small-diameter neck portion.
In accordance with another embodiment of the present invention, there is provided a projection type cathode ray tube device comprising: a glass envelope including a panel, a neck, a funnel connecting the panel to an end of the neck, and a stem closing another end of the neck; a phosphor screen formed on an inner surface of the panel; an electron gun housed in the neck for projecting an electron beam toward the phosphor screen; a deflection yoke for scanning the electron beam on the phosphor screen; and a convergence yoke for generating a beam-convergence magnetic field, wherein the neck comprises a large-diameter neck portion disposed on a side thereof facing toward the stem, and a neck junction region having an outside diameter thereof decreasing toward the funnel, one end of the neck junction region being connected to the large-diameter neck portion, and another end of the neck junction region being connected to the funnel, the deflection yoke is disposed in a vicinity of a transition region between the funnel and the neck junction region, and the convergence yoke is disposed to extend from the large-diameter neck portion and surround at least a portion of the neck junction region.